JP2005117665A - Air-gap type fbar, method of manufacturing the same, and filter and duplexer using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for fabricating an air-gap type FBAR, FBAR manufactured by the method, and to provide a filter and duplexer which uses the same. <P>SOLUTION: The air-gap type FBAR includes a first substrate having a cavity part at a predetermined region on its upper surface; a dielectric film stacked on the upper part of the substrate; a first air gap formed between the first substrate and the dielectric film; a stacked resonance part including a lower electrode/piezoelectric layer/upper electrode formed on the upper part of the dielectric film; a second substrate having a cavity part at a predetermined region on its lower surface and joined to the first substrate; and a second air gap formed between the stacked resonance part and the second substrate. A thin film, having predetermined thickness made of a liquid crystal polymer (LCP), may be used as the dielectric film. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an FBAR (Film Bulk Acoustic Resonator) that can be used for filters, duplexers, and the like for RF (Radio Frequency) band communication, and more specifically, by using a liquid crystal polymer (LCP) thin film film. The present invention relates to a stable air gap (Air-Gap) type FBAR, a manufacturing method thereof, and a filter and a duplexer using the same.

  In recent years, wireless mobile communication technology has been remarkably developed. Such mobile communication technology requires various RF components that can efficiently transmit information in a limited frequency band. In particular, a filter among RF components is one of the core components used in mobile communication technology, and a signal desired by a user is selected from countless aerial waves or a signal to be transmitted is filtered. By doing so, it becomes possible to perform high-quality communication.

  At present, typical RF filters for wireless communication include dielectric filters and SAW (Surface Acoustic wave) filters. Dielectric filters have the advantages of high dielectric constant, low insertion loss, stability at high temperature, and resistance to vibration and shock. However, the dielectric filter has a limit in miniaturization and MMIC (Monolithic Microwave IC) which are recent technological development trends. In addition, the SAW filter is advantageous in that it is small in size as compared with the dielectric filter, can easily perform signal processing, has a simple circuit, and can be mass-produced by using a semiconductor process. Further, the SAW filter has an advantage that high-quality information exchange can be performed because side rejection in the pass band is higher than that of the dielectric filter. However, since the SAW filter process includes a process of performing exposure using ultraviolet rays (UV), there is a disadvantage that an IDT (InterDigital Transducer) line width is about 0.5 μm. Therefore, there is a problem that it is not possible to cover a super high frequency (5 GHz or higher) band using a SAW filter, and it is fundamentally impossible to be configured on a single chip with an MMIC structure on a semiconductor substrate. is there.

  In order to overcome the limitations and problems described above, an FBAR has been proposed that can be integrated with other active devices on an existing semiconductor (Si, GaAs) substrate and the frequency control circuit can be made completely MMIC.

  The FBAR is a thin film element that is low in cost and small in size, and can realize characteristics of a high quality (High Q) coefficient. Therefore, the FBAR is a wireless communication device and a military radar in various frequency bands (900 MHz to 10 GHz). Can be used. Further, the size can be reduced to one hundredth of the size of dielectric filters and lumped constant (LC) filters, and the insertion loss is much smaller than that of SAW filters. Therefore, FBAR can be applied to MMICs that are highly stable and require a high quality factor.

  FBAR is made by a semiconductor process using a sandwich structure such as an upper electrode, a piezoelectric body, and a lower electrode, generates a piezoelectric phenomenon, and generates resonance in a certain frequency band. When the frequency of the wave is equal to the frequency of the input electrical signal, a resonance phenomenon occurs. A resonator using such a resonance phenomenon is made into an electrical coupling phenomenon to produce an FBAR filter, and a duplexer using the FBAR filter can be realized.

The FBAR structure has been studied in various forms. In the membrane type FBAR, a silicon oxide film (SiO ₂ ) is vapor-deposited on a substrate, and a membrane layer is formed on the opposite surface via a cavity formed by anisotropic etching (Isotropic Etching). Also, a lower electrode is formed on the silicon oxide film, a piezoelectric material is deposited on the lower electrode layer by RF magnetron sputtering to form a piezoelectric layer, and an upper electrode is formed on the piezoelectric layer. .

  Such a membrane-type FBAR has the advantages of low substrate dielectric loss and low power loss due to the cavity. However, the membrane type FBAR has a problem that the yield is reduced due to breakage because the element occupies a large area due to the directivity of the silicon substrate and the structural stability is low in the subsequent packaging process. Therefore, recently, air gap type and Bragg reflector type FBARs have appeared to reduce the loss caused by the membrane and to simplify the device manufacturing process.

  The Bragg reflection type FBAR has a structure in which a substance having a large difference in elastic impedance is deposited on a substrate every other layer to form a reflection layer, and a lower electrode, a piezoelectric layer, and an upper electrode are laminated in order, and pass through the piezoelectric layer. The elastic wave energy is not transmitted in the direction of the substrate but is totally reflected by the reflective layer so that efficient resonance is generated. Such a Bragg reflection type FBAR is structurally robust and free from stress due to warping, but it is difficult to form a reflective layer of four or more layers having a precise thickness for total reflection. There is a disadvantage that it takes a lot.

  Note that the conventional air gap type FBAR having a structure in which the substrate and the resonance portion are separated by using an air gap instead of the reflective layer, the anisotropic etching is performed on the surface of the silicon substrate 100 as shown in FIG. After forming the sacrificial layer and polishing the surface by CMP, the insulating layer 120, the lower electrode 133, the piezoelectric layer 135, and the upper electrode 137 are sequentially deposited, the sacrificial layer 110 is removed through the via hole, and the air gap 140 FBAR is realized by forming.

  However, the fabrication of the conventional FBAR as described above requires a CMP process, which complicates the process and increases the unit price, and uses wet etching to remove the sacrificial layer and form an air gap. However, in this case, it is difficult to remove the etching solution, and if the etching solution cannot be removed completely, the remaining etching solution weakens the element and induces a change in resonance frequency. Even when dry etching is performed, there are problems such as physical impact that ions, molecules, etc. in the plasma state exert on the device and deterioration due to high heat when performing existing plasma dry etching.

  An object of the present invention is to realize a simple and robust FBAR. Another object of the present invention is to realize a filter and a duplexer using the air gap type FBAR according to the above-described method.

  An air gap type FBAR of the present invention for achieving the above-mentioned object is provided for forming a first substrate having a cavity in a predetermined region on the upper surface and a first air gap in the cavity of the first substrate. A dielectric film laminated on the first substrate; a laminated resonance part formed of a lower electrode, a piezoelectric layer, and an upper electrode on the dielectric film; and a cavity in a predetermined region on the lower surface, And a second substrate bonded to the first substrate. Thus, in manufacturing an air gap type FBAR, a dielectric film is stacked on a silicon substrate having a cavity, and an air gap is formed without performing a CMP step and a step of removing a sacrificial layer. By reducing the impact on the device due to the dry etching process and reducing the process steps and process errors, a simple and robust FBAR can be realized.

  The dielectric film is formed by using a thin film having a predetermined thickness formed of liquid crystal polymer (LCP) or etching a thin film formed of liquid crystal polymer (LCP) to a predetermined thickness. be able to. The dielectric film may be formed by etching a thin film formed of liquid crystal polymer (LCP) only to a predetermined area corresponding to the first air gap to a predetermined thickness. .

  The method of manufacturing an air gap type FBAR according to the present invention includes a step of forming a first air gap by stacking a dielectric film on a first substrate having a cavity in a predetermined region on the upper surface, and an upper portion of the dielectric film. Forming a laminated resonance portion on the surface; and joining a second substrate having a cavity in a predetermined region of the first substrate and the lower surface to form a second air gap.

  The step of forming the laminated resonance part includes depositing a lower electrode on a predetermined region of the upper surface of the dielectric film and depositing a piezoelectric layer on the upper surface of the lower electrode corresponding to the cavity of the first substrate. And depositing an upper electrode on the upper surface of the piezoelectric layer and an upper surface of a predetermined region of the dielectric film on which the lower electrode is not deposited.

  Preferably, in the step of forming the first air gap, a thin film having a predetermined thickness made of liquid crystal polymer (LCP) is used as the dielectric film.

  The air gap type FBAR filter according to the present invention has a first resonance part formed by connecting a plurality of FBARs having a first resonance frequency in series, a second resonance frequency, and the first resonance frequency. A second resonating unit formed of a plurality of FBARs connected in parallel to a plurality of FBARs of the unit, and a plurality of inductors respectively connected in series to the plurality of FBARs forming the second resonating unit, Each of the FBARs constituting the first and second resonating portions includes a dielectric film stacked on top of a first substrate having a plurality of cavities on the upper surface, and between the first substrate and the dielectric film. A first air gap is formed, and a laminated resonance part formed of a lower electrode, a piezoelectric layer, and an upper electrode on the dielectric film.

  As the dielectric film, a thin film having a predetermined thickness made of liquid crystal polymer (LCP) is used.

  An air gap type FBAR duplexer according to the present invention includes a first FBAR filter for transmitting a signal input to a transmission terminal via an antenna, and a signal received via the antenna to a reception terminal. The second FBAR filter is formed, and is formed between the antenna and the second filter, and changes the phase of a signal to be transmitted / received to reduce signal interference in the first filter and the second filter. And the first and second filters have first and second resonating parts each having a predetermined resonance frequency different from each other, and the first and second resonating parts are included in the first and second resonating parts. Each of the plurality of FBARs formed includes a dielectric film stacked on top of a first substrate having a plurality of cavities on the upper surface, and a gap between the first substrate and the dielectric film layer. Comprising a first air gap is formed, and a laminated resonance part which said the upper part of the dielectric film is formed in the lower electrode, the piezoelectric layer, the upper electrode.

  In the air gap type FBAR according to the present invention, a liquid crystal polymer (LCP) thin film is laminated on a silicon substrate having a cavity, and an air gap is easily formed without performing a CMP step and a step of removing a sacrificial layer. Therefore, the process steps and process errors can be reduced, the manufacturing process is simpler than the existing FBAR manufacturing process, the time required for the manufacturing process is shortened, and the resonance characteristics are improved. Further, by using an air gap type FBAR made according to the present invention, it is possible to realize an improved FBAR filter and duplexer with a simpler process.

  Hereinafter, the FBAR of the present invention and the manufacturing process thereof will be described in detail with reference to the accompanying drawings.

  FIG. 2 is a cross-sectional view showing the manufacturing process of the air gap type FBAR according to the present invention step by step. The air gap type FBAR according to the present invention includes a first substrate 200, a second air gap 210, a dielectric film 220, a laminated resonance unit 230, a second substrate 240, and a second air gap 250.

First, the first substrate 200 having a cavity portion can be formed by anisotropically etching a predetermined region on the upper surface of the silicon substrate, that is, a region corresponding to the stacked resonance unit 230 to a depth of 2 to 3 μm ( FIG. 2 (a))
The first air gap 210 is formed by laminating a dielectric film 200 having a predetermined thickness on the first substrate 200. This dielectric film supports the laminating resonance part 230 and serves as an insulating layer. Then, a thin film made of a polymer such as LCP (Liquid Crystal Polymer) is used (FIG. 2B). In this case, the LCP thin film is used after being polished to a thickness of about 1 μm, or a film having a thickness of about 1 μm from the beginning can be used. Further, after laminating a 5 μm LCP thin film on the first substrate, PR is deposited to a thickness of 5 to 10 μm, and a portion corresponding to the first air gap is etched to a thickness of about 1 μm. (FIG. 2 (c)). In the present invention, the dielectric film on which the PR is not deposited is etched by a dry etching method.

  The laminated resonance unit 230 is formed on the dielectric film 220. The lower electrode 233, the piezoelectric layer 235, and the upper electrode 237 are sequentially deposited and formed in a certain region including a portion corresponding to the first air gap. (FIG. 2 (d)). When an external signal is applied between the two electrodes, part of the electrical energy input between the two electrodes is converted into mechanical energy due to the piezoelectric effect, which is converted back into electrical energy. In the process, resonance occurs with respect to the frequency of the natural vibration due to the thickness of the piezoelectric layer 235. In addition, mutually different resonant frequencies can also be obtained by making the thickness of the LCP thin film different.

  When the lower electrode 233 is deposited, if the first air gap 210 is positioned under the laminated resonance part 230 where resonance occurs directly at one end of the dielectric film 220, the substrate is isolated and the resonance efficiency is improved. Therefore, the lower electrode 233 needs to be patterned so as to cover the upper layer of the first air gap 210. As the lower electrode, a normal conductive material such as metal is used, but preferably aluminum (Al), tungsten (W), gold (Au), platinum (Pt), nickel (Ni), titanium (Ti). One can be selected from the group of chromium (Cr), palladium (Pd) and molybdenum (Mo).

  In the next step, a piezoelectric layer 235 is deposited on a predetermined region of the lower electrode 233 and the dielectric layer 130. As a normal piezoelectric material, aluminum nitride (AlN) or zinc oxide (ZnO) is used, but is not limited thereto. As the vapor deposition method, any one of an RF magnetron sputtering method and an evaporation method can be used. After the piezoelectric layer 235 is deposited on the lower electrode 233, it is necessary to pattern the piezoelectric layer 235 so as to cover the upper layer where the air gap 210 is located in the lower portion, like the lower electrode 233.

  In the next step, an upper electrode 237 is deposited on the piezoelectric layer 235 and the dielectric film 220. The upper electrode 237 may use the same material, the same vapor deposition method, and the same patterning method as the lower electrode 233.

  Next, the second substrate 240 having a cavity in a predetermined region is bonded to the first substrate 200 having the laminated resonance portion, and then a plurality of vias for connection with an external signal are formed (FIG. 2 (e)).

  Thus, when manufacturing an air gap type FBAR, a liquid crystal polymer (LCP) thin film is laminated on a silicon substrate having a cavity, and an air gap is formed without performing a CMP step and a step of removing a sacrificial layer. By doing so, it is possible to realize a simple and robust FBAR by reducing the impact on the element due to the existing dry etching process and reducing the process steps and process errors.

  Using the air gap type FBAR made as described above, the FBAR filter can be realized by circuitizing the serial FBAR and the parallel FBAR in a ladder shape. The pass band of the filter is determined by the resonance characteristics of the respective FBARs constituting the circuit.

  The FBAR filter includes a plurality of FBARs having a first resonance part formed of a plurality of FBARs having a first resonance frequency, a second resonance frequency, and being connected in parallel to the plurality of FBARs of the first resonance part. And a plurality of inductors connected in series to a plurality of FBARs forming the second resonance part and the second resonance part.

  FIG. 3 is a cross-sectional view showing the first resonance unit 3A and the second resonance unit 3B of the air gap type FBAR filter according to the present invention. In this filter, a first air gap 310a, 310b is formed by laminating an LCP thin film 320 on a substrate 300 having a plurality of cavities, and a lower electrode 333, a piezoelectric layer 335a, 335b, an upper portion are formed on the dielectric film 320. After electrodes 337a and 337b are sequentially deposited to form a laminated resonance part, a second substrate 360 having a cavity is joined to the upper part of the first substrate, and vias 360a and 360b for connection with external signals are formed. Realized by forming.

  FIG. 4 is a simplified structural diagram of an air gap type FBAR duplexer according to the present invention. In the drawing, the basic structure of an FBAR duplexer that appropriately branches a signal transmitted and received via one antenna connected to 450b is roughly composed of a transmission end filter 410, a reception end filter 420, and a phase change unit 430. The transmission end filter 410 and the reception end filter 420 are band-pass filters that allow only frequencies to be transmitted and received to pass through. The frequency of signals transmitted and received through the transmission / reception end filters 410 and 420 has a slight difference, but the transmission / reception end filters 410 and 420 are isolated from each other when they are sensitive to mutual interference. Thus, the phase change unit 430 that prevents the mutual interference is required. The phase changing unit 430 normally performs phase shift using a capacitor and an inductor so that the phase difference between the transmission and reception signals has 90 degrees to prevent mutual interference.

  The preferred embodiments of the present invention have been described above with reference to the drawings. However, the scope of protection of the present invention is not limited to the above-described embodiments, and is shown by the claims. There are no restrictions on the text of the description. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

  The present invention is applied to a filter, a duplexer, and the like for performing communication in the RF band.

It is process drawing which shows the manufacture process of the conventional air gap type FBAR according to a stage. It is process drawing which shows the manufacture process of the air gap type FBAR which concerns on one Example of this invention according to a step. It is a structural diagram showing a filter using an air gap type FBAR according to the present invention. It is a figure which shows the schematic structure of the duplexer using the air gap type FBAR which concerns on this invention.

Explanation of symbols

200 First substrate 210 First air gap 220 Dielectric film 230 Laminated resonance part 233 Lower electrode 235 Piezoelectric layer 237 Upper electrode 240 Second substrate 250 Second air gap 310a, 310b First air gap 320 Dielectric film 333 Lower electrode 335a, 335b Piezoelectric layer 337a, 337b Upper electrode 410 Transmission end filter 420 Reception end filter 430 Phase change section

Claims (10)

A first substrate having a cavity in a predetermined region on the upper surface;
A dielectric film stacked on top of the first substrate to form a first air gap in the cavity of the first substrate;
A laminated resonance part formed of a lower electrode, a piezoelectric layer, and an upper electrode on the dielectric film;
A second substrate having a cavity in a predetermined region on the lower surface and bonded to the first substrate;
An air gap type FBAR characterized by comprising:   2. The air gap type FBAR according to claim 1, wherein the dielectric film is a thin film having a predetermined thickness made of liquid crystal polymer (LCP).   The air gap type FBAR according to claim 1, wherein the dielectric film is formed by etching a thin film made of liquid crystal polymer (LCP) to a predetermined thickness.   The dielectric film is formed by locally etching a thin film formed of liquid crystal polymer (LCP) to a predetermined thickness only in a predetermined region corresponding to the first air gap. Item 2. The air gap type FBAR according to Item 1. Forming a first air gap by laminating a dielectric film on a first substrate having a cavity in a predetermined region on the upper surface;
Forming a laminated resonance part on the upper surface of the dielectric film;
Bonding a first substrate and a second substrate having a cavity in a predetermined region on the lower surface to form a second air gap;
The manufacturing method of the air gap type FBAR characterized by including. The step of forming the laminated resonance part includes
Depositing a piezoelectric layer on the upper surface of the lower electrode corresponding to the cavity of the first substrate;
Depositing an upper electrode on the upper surface of the piezoelectric layer and an upper surface of a predetermined region of the dielectric film on which the lower electrode is not deposited;
The manufacturing method of the air gap type FBAR of Claim 5 characterized by the above-mentioned.   6. The air according to claim 5, wherein, in the step of forming the first air gap, a thin film having a predetermined thickness formed of liquid crystal polymer (LCP) is used as the dielectric film. Gap type FBAR manufacturing method. A first resonance part formed by connecting a plurality of FBARs having a first resonance frequency in series;
A second resonating unit having a second resonance frequency and formed of a plurality of FBARs connected in parallel to the plurality of FBARs of the first resonating unit;
A plurality of inductors connected in series to a plurality of FBARs forming the second resonating unit,
The respective FBARs constituting the first and second resonating parts are:
A dielectric film stacked on top of the first substrate to form a first air gap above the first substrate having a plurality of cavities on the top surface;
A laminated resonance part formed of a lower electrode, a piezoelectric layer, and an upper electrode on the dielectric film;
An air gap type FBAR filter.   9. The air gap type FBAR filter according to claim 8, wherein a thin film having a predetermined thickness formed of liquid crystal polymer (LCP) is used as the dielectric film. A first FBAR filter for transmitting a signal input to the transmission terminal via the antenna;
A second FBAR filter that allows a signal received via the antenna to be input to a receiving terminal;
A phase change unit that is formed between the antenna and the second filter, changes a phase of a signal transmitted and received, and prevents signal interference in the first filter and the second filter;
The first and second filters are:
Each of the plurality of FBARs formed in the first and second resonance units has a plurality of cavities on the upper surface. The first and second resonance units each have a predetermined resonance frequency different from each other. A dielectric film stacked on top of the first substrate to form a first air gap on the top of the one substrate;
A laminated resonance part formed of a lower electrode, a piezoelectric layer, and an upper electrode on the dielectric film;
An air gap type FBAR duplexer comprising:

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